1. Field of the Invention
The present invention relates to an apparatus for monitoring quality of a picture in transmission that is preferable to collectively remote-monitor at a center the picture or video picture quality at a plurality of transmission processing positions disposed in sequence in a transmission path.
2. Description of the Related Art
As a conventional method of automatically monitoring and assessing video picture quality, there are available (1) a method of comparing a processed picture with its original picture, (2) a method of assessing picture quality based on only a processed picture, and (3) a method of comparing the characteristic value of an original picture with that of a processed picture.
An example of the method (1) is disclosed in detail in, for example, the following document. T. Hamada. et al. “Picture quality assessment system by three-layered bottom-up noise weighing considering human visual perception”, SMPTE Journal, Vol. 108, No. 1, January 1999.
However, it is impossible to use the above method (1) in the actual field of picture transmission. This is because it is only a processed picture that can be obtained and an original picture cannot be used, during the actual transmission of a picture.
Thus, conventionally, only the method (2) or (3) can be substantially employed to monitor and assess the quality of a picture in transmission. However, the precision of assessment of the method (2) is low in principle because it assesses picture quality based on only a processed picture. In contrast, the method (3) can realize monitoring of picture quality with higher precision than the method (2) because in this method some characteristic value of an original picture is transmitted from a transmission side through a low speed transmission path and compared with the same characteristic value on a reception side.
An invention according to the method (3) is filed by the inventors as Japanese Patent Application No. 2000-256015 titled “Apparatus for assessing quality of picture in transmission and apparatus for remote-monitoring quality of picture in transmission”.
In the method (3), it is important to assess picture quality as precisely as possible based on a characteristic value of an amount as small as possible. In particular, while it is important to assess a mean square error (hereinafter, abbreviated as “MSE”) that is as a base of picture quality assessment, there has been announced neither an apparatus nor a method of assuming the MSE based on a small amount of characteristic value.
The MSE is defined here as follows. When a signal on a transmission side is shown by x(t), a (deteriorated)signal on a reception side is shown by y(t), and the total number of pixels is shown by N, the MSE can be expressed by the following formula (1).MSE=1/N·Σ[X(t)−y(t)]2  (1)
In the above formula (1), t shows a two-dimensional coordinate composed of horizontal and vertical coordinate axes. A sum is determined as to all the pixels.